1. Field of the Invention
This invention relates to a novel liquid crystal compound. More particularly it relates to a chiral liquid crystal compound having an optically active group and a chiral liquid crystal composition containing the same.
The liquid crystal compound referred to herein includes not only substances which liquid crystal state can be observed by themselves, but also those which liquid crystal state cannot be observed by themselves and nevertheless which have a similar chemical structure to those of liquid crystal compounds and are suitable as a component constituting liquid crystal compositions.
2. Description of the Related Art
At present, TN (Twisted Nematic) mode display has been most broadly employed for liquid crystal display elements. This TN liquid crystal display has many advantages such as low driving voltage, small power consumption, etc. However, the elements are inferior in the aspect of response rate to emissive mode display elements such as those of cathode ray tube, electroluminescence, plasma display, etc. A new TN mode display element having the twist angle increased from conventional 90.degree. up to 180.degree..about.270.degree. has also been developed, but it is still inferior in the response rate. As described above, various efforts for improvement has been made, but such efforts have not yet fruitful. On the other hand, a new display mode using ferroelectric liquid crystals has a possibility of notably improving the response rate (Clark et al; Applied Phys. lett., 36, 899 (1980)). This mode is directed to a method of making use of chiral smectic phases such as chiral smectic C phase (hereinafter abbreviated to SC*) exhibiting ferroelectric properties. It has been known that phases exhibiting ferroelectric properties are not limited only to SC* phase, but chiral smectic F, G, H, I, etc. phases also exhibit ferroelectric properties. However, for making practical use of ferroelectric liquid crystal display elements, a number of characteristics have been required for liquid crystal materials used therefor.